Yuan G, Gu Y
Department of Pathophysiology, Nantong Medical College, Qixiou Road 19, Nantong 226001, China.
Chin Med J (Engl). 1999 Jun;112(6):546-9.
To examine whether growth hormone (GH) promotes the phosphorylation of epidermal growth factor (EGF) receptor and to elucidate the mechanisms by which EGF receptors were transactivated by GH stimulation.
Cultured cardiac myocytes were stimulated by GH directly or pretreated with inhibitors before GH stimulation. The phosphorylations of EGF receptor and JAK2 were examined with immunoprecipitation followed by Western blotting using anti-phosphotyrosine antibody (4G10). The activities of extracellular signal-regulated kinases (ERKs) were assayed with the method of MBP-containing gel.
GH stimulated phosphorylation of EGF receptor in a time-dependent manner. Tyrphostin AG1478, a selective inhibitor of EGF receptor, strongly suppressed GH-induced ERK activation, while tyrphostin AG1295, a selective inhibitor of PDGF receptor, had no effects on the activation of ERKs stimulated by GH in cardiac myocytes. In addition, GH induced tyrosine phosphorylation of JAK2, a cytoplasmic protein tyrosine kinase, in cardiac myocytes. Moreover, tyrphostin B42, an inhibitor of JAK2 suppressed GH-induced phosphorylation of EGF receptor as well as GH-induced activation of ERKs in cardiac myocytes.
GH evokes the phosphorylation of EGF receptor in cardiac myocytes through activating JAK2. Phosphorylated EGF receptor plays a critical role in GH signaling pathway leading to ERK activation in cardiac myocytes.
研究生长激素（GH）是否促进表皮生长因子（EGF）受体的磷酸化，并阐明GH刺激激活EGF受体的机制。
对培养的心肌细胞直接给予GH刺激，或在GH刺激前用抑制剂预处理。采用免疫沉淀法，随后用抗磷酸酪氨酸抗体（4G10）进行蛋白质免疫印迹，检测EGF受体和JAK2的磷酸化情况。采用含髓鞘碱性蛋白（MBP）凝胶法检测细胞外信号调节激酶（ERK）的活性。
GH以时间依赖性方式刺激EGF受体的磷酸化。EGF受体选择性抑制剂酪氨酸磷酸化抑制剂AG1478强烈抑制GH诱导的ERK激活，而血小板衍生生长因子（PDGF）受体选择性抑制剂酪氨酸磷酸化抑制剂AG1295对心肌细胞中GH刺激的ERK激活无影响。此外，GH诱导心肌细胞中细胞质蛋白酪氨酸激酶JAK2的酪氨酸磷酸化。而且，JAK2抑制剂酪氨酸磷酸化抑制剂B42抑制心肌细胞中GH诱导的EGF受体磷酸化以及GH诱导的ERK激活。
GH通过激活JAK2引起心肌细胞中EGF受体的磷酸化。磷酸化的EGF受体在心肌细胞中导致ERK激活的GH信号通路中起关键作用。
